In the prior art, two types of schemes, namely the centrifugation technology and the wedge technology, are employed to prepare blood smears, which are to be observed with a microscope.
A process employing the centrifugation technology comprises the following steps, placing a microscope slide in a sealed container having a rotatable disc, dropping blood onto the microscope slide, rotating the rotatable disc to drive the microscope slide to rotate together so as to swing off redundant blood, such that a blood film of monolayer cell is formed on the surface of the microscope slide. However, this technology has the following disadvantages: 1) the interior of the container is contaminated each time after a blood smear is prepared, and it is difficult to clean the container automatically, and 2) although a shield may be provided outside the rotatable disc to form the sealed environment, a large amount of floating blood particles (floating masses) are generated within the shield during a high speed rotating period, and the shield is unable to prevent the floating masses from diffusing into the air, and the blood, if it is pathogenic, would put the lab staffs in great danger. Even though the above problems could be solved, it will result in high production cost and thus is impractical.
Referring to FIG. 1, a process employing the wedge technology comprises the following steps. First, a certain amount of blood 9 is dripped onto a microscope slide 8 at the position A. Secondly, blood 9 is contacted by an edge of a spreader 7, such that blood 9 is diffused along the edge of the spreader 7 (at the position B). At last, the spreader 7 draws blood 9 such that the suction among the blood cells drives the blood to form a uniform blood film on the microscope slide 8 (at positions C and D). Such a process utilizing a spreader has the advantages of being not harmful to the environment and the operator, easy to implement and low in cost.
Comparing the above two schemes with respect to each other, one may find that it is more practical to use the wedge technology to prepare blood smears. Prior art blood smear preparation device employing the wedge technology comprises a spreader retaining plate, a spring mounting rack, a stand for supporting a front end of a spreader and a moving rod for moving the front end of the spreader. The spreader retaining plate is used for retaining the spreader. The spring mounting rack is used for mounting a tension spring, which generates a tension force when the whole spreader retaining means descends to make the spreader contact the microscope slide, such that the spreader presses against the microscope slide with a predetermined pressure. The spreader retaining plate is able to pivot about a pivot point. Two tension springs are fixed to the spreader retaining plate symmetrically. When the whole spreader retaining means descends to make the spreader contact the microscope slide, the spreader pivots about the pivot point in a clockwise direction to pull the two springs downward such that its reaction force makes the spreader to press against the microscope slide with a pressure. Meanwhile, another spring is used to limit the front end of the spreader so as to prevent the spreader retaining plate from pivoting downward about the pivot point without limit when the spreader is in a suspending state. The stand for supporting the front end of the spreader is used to fix the spreader retaining plate and the spring mounting rack. The moving rod for moving the front end of the spreader may drive the spreader retaining plate, the spring mounting rack and the stand for supporting the front end of the spreader to move upward and downward as well as forward and backward. The moving rod may be connected to the stand through a connecting shaft, such that they may rotate about the connecting shaft clockwise and counterclockwise.
However, such a preparation device has the following disadvantages.
1) The structure of the spreader retaining means of the device is complicated and has a high possibility of failure. Since the pressure is adjusted by means of two tension springs, it is difficult to adjust initial tension forces at the time of mounting the springs. Further, another spring is used to limit the front end of the spreader, such that the spreader retaining plate is prevented from pivoting downward about the pivot point without limit when the spreader is is in a suspending state. Since there are too many springs to be used, the possibility of spring failure is increased. In an automatic spreading and dyeing device, the spreader retaining means has the higher possibility of failure when preparing a smear with a spreader, and such a failure is mainly due to spring failure.
2) With respect to the structure of the spreader retaining means, because the spreader presses against the spreader retaining plate tightly and directly, it is impossible to adjust relative positions between the spreader and the microscope slide, and thereby it is impossible to ensure that the edge of the spreader is perpendicular to a long edge of the microscope slide. Manufacture and assembly errors of the front end of the spreader may result in that a short edge of the spreader is not perpendicular to the long edge of the microscope slide, which in turn causes such problems that the blood film is not at the center of the microscope slide, that there is a delay in the movement of the spreader and so on. These problems will affect the quality of the smear adversely.
3) The blood smear preparation device has no good damping capability. As a result, the blood smear has grainy streaks in a longitudinal direction, which will affect the clinical observation unfavorably.